AMD's Carrizo Aims for Better Energy Efficiency

It's an interesting chip, which takes the same basic concepts as the earlier Kaveri chip and uses the same 28nm process, but adds in a number of advances particularly aimed at making the chip more energy-efficient, and thus better suited for lower-power devices.

Earlier this week, AMD gave a lot of new details on its upcoming mainstream chips for laptops and low-all-in-ones for 2015, code-named Carrizo (and likely to be sold mostly under the A-series moniker). It's an interesting chip, which takes the same basic concepts as the earlier Kaveri chip and uses the same 28nm process, but adds in a number of advances particularly aimed at making the chip more energy-efficient, and thus better suited for lower-power devices.

Although AMD has previously said the chip would be available this year, it covered a lot more details in a presentation at the International Solid State Circuits Conference (ISSCC), which is happening this week in San Francisco.

As AMD has been pushing for years, Carrizo is what the company calls an accelerated processing unit (APU), which means it combines the CPU, graphics (GPU), and other capabilities (such as multimedia processing) into a single chip. This was unusual when AMD first announced the strategy, but now it's fairly commonplace, in PC and mobile chips.

But within the concept, Carrizo takes this further. It is the first processor designed to be "fully HSA compliant," meaning that workloads can use the CPU or GPU with the same memory system, following specifications for Heterogeneous Systems Architecture (HSA), agreed to by the HSA Foundation, a group including AMD, ARM, Imagination Technologies, MediaTek, Qualcomm, Samsung, and Texas Instruments. The idea is that by using the GPU to compute some calculations that used to be done on the CPU (such as video indexing, pattern recognition, and natural user interface), the system can offer better performance and low energy per operation.

Much of the other improvements involve using less die area for specific components, through a higher-density design. In total, AMD says Carrizo will have 29 percent more transistors in nearly the same die size as its predecessor (known as Kaveri), despite using the same 28nm process. In total, the chip will have 3.1 billion transistors and will consume 250 mm2.

On the CPU side, Carrizo includes new CPU cores called "Excavator." These seem to be a variation of the earlier "Steamroller" x86 cores, with the same basic architecture in which a pair of integer cores shares Level 2 cache and some other features. AMD said this allowed for a 23 percent reduction in the area of the chip consumed by the cores, while offering 5 percent improvement in instructions per clock, and consuming lower power.

In addition, there are eight new Radeon GPU cores, which AMD said allows 10 percent higher frequency at the same power level, or up to 20 percent lower power at the same frequency. The chip also has voltage adaptive features, which again save power. Other features include an on-chip H.265 video decoder, and a claimed 3.5 times faster transcode performance. Most interestingly, the chip includes an integrated "southbridge" – the part of the chip that typically connects most input/output (I/O) ports to the chip. (Intel now calls this a platform controller hub or PCH.) This is unusual for a PC chip.

While not announcing future processors, AMD did show a series of improvements it is working on going forward, most aimed at energy optimization. Overall, the company said it hopes to improve the energy efficiency of its mobile platforms by at least 25 times by 2020.

Overall, AMD said Carrizo would offer "double digit" increases in performance and battery life. All of this sounds very good, and it might allow AMD to play in some lower-power scenarios than the previous generation. (Almost all the Kaveri implementations I saw were in relatively larger laptops and desktops).

Of course, Carrizo will square off against Intel's 14nm Atom (Cherry Trail) and Core (Broadwell) families this year. Intel has a process lead with its 14nm FinFET manufacturing, and thus the Atom chips should be less expensive, while Broadwell should offer higher CPU features. But AMD has offered better integrated graphics and now has some new features such as the HSA support that might prove interesting. I'll be interested in testing out some Carrizo systems to see if AMD really has closed the gap.

Michael J. Miller's Forward Thinking Blog: forwardthinking.pcmag.com
Michael J. Miller is chief information officer at Ziff Brothers Investments, a private investment firm. From 1991 to 2005, Miller was editor-in-chief of PC Magazine, responsible for the editorial direction, quality and presentation of the world's largest computer publication.
Until late 2006, Miller was the Chief Content Officer for Ziff Davis Media, responsible for overseeing the editorial positions of Ziff Davis's magazines, websites, and events. As Editorial Director for Ziff Davis Publishing since 1997, Miller took an active role in...
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